Iran's Foreign Minister Mohammad Javad Zarif said Sunday that US President Donald Trump's decision to ban arrivals from seven Muslim majority countries was "a great gift to extremists".
"#MuslimBan will be recorded in history as a great gift to extremists and their supporters," Zarif said as part of a string of tweets.
"Collective discrimination aids terrorist recruitment by deepening fault-lines exploited by extremist demagogues to swell their ranks."
Trump on Friday signed a sweeping executive order to suspend refugee arrivals and bar visas for travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.
Iran's foreign ministry had earlier released a statement saying it would reciprocate with a ban on Americans entering the country.
But Zarif added that its restrictions would not apply to Americans who already have a valid visa.
"Unlike the US, our decision is not retroactive. All with valid Iranian visa will be gladly welcomed," he wrote.
With more than one million Iranians living in the United States, the travel restrictions are expected to cause chaos for students, businessmen and families travelling between the two countries.
Parliament speaker Ali Larijani said the measures were proof of America's "violent racist spirit".
The foreign ministry released a travel advisory, calling on all citizens travelling to the US to "make completely sure" before leaving that they will not face obstacles.
Travel agents in Tehran said Saturday they had been instructed by foreign airlines, including Emirates, Etihad and Turkish Airlines, not to sell US tickets and that Iranians holding American visas were not being allowed to board US-bound flights.